Pneumatic tire manufacturing method, and pneumatic tire

ABSTRACT

A pneumatic tire manufacturing method is provided in which raw cover molding is suitably performed with no, or a minimal amount of, down-stitching in the manufacture of SOT-structure pneumatic tires; also provided is a pneumatic tire. This pneumatic tire manufacturing method involves: a step in which a sidewall, an inner liner, and a ply are bonded on a first molding drum, a pair of beads is set, and the tread side part is formed on the side wall, forming a first cover; a step in which a breaker and band are bonded on a second molding drum and the tread center part is formed on the band, shaping the tread ring; a step in which the first cover is inserted inside of the tread ring and the first cover is inflated, bonding the tread ring and the first cover with pressure; and a step in which the sidewall is folded back towards the lateral surface of the inflated first cover and bonded to the lateral surface of the first cover, and the tread side part and the tread center part are bonded together.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a pneumatictire having a so-called SOT (Sidewall Over Tread) structure, havingsidewalls formed to cover tread ends, and to a pneumatic tiremanufactured using this method.

BACKGROUND ART

Generally, a pneumatic tire having the SOT structure has its low coverformed in two steps.

Specifically, first, a sidewall is wrapped on opposite side portions ofa first forming drum and, thereafter, on the central portion of thefirst forming drum, an inner liner and a ply are pasted successively.Then, a pair of beads is set inside the sidewalls, at positionscorresponding to the width of the tire product. Thus, the first cover isformed (first cover forming step).

On the other hand, in parallel with the formation of first cover, on asecond forming drum, a breaker and a band such as JLB (jointless band)are pasted and thereafter, a tread is wrapped by strip-winding, wherebya tread ring is formed (tread ring forming step).

Then, the first cover is inserted to the inside of tread ring, and thatportion of the first cover which is between the beads is inflated andpressure-bonded to the tread ring, to form a shape close to that of thelow cover (shaping step).

Thereafter, in order that the tread is pressure-bonded to the firstcover with no gap left therebetween, sides of tread are pressed by usinga stitcher so that the sides extend along a curved side surface of thefirst cover that has been pressure-bonded to the tread ring (stitch-downstep).

Thereafter, the sidewall outer than the bead is turned up toward theside surface of inflated first cover, and the sidewall is pasted tocover the tread end (turn-up step). In this manner, the first cover andthe tread ring are integrated and the formation of low cover iscompleted (for example, see Patent Documents 1, 2).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-2013-39695

Patent Document 2: JP-A-2013-188866

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The above-described stitch-down step, however, is a step of making thetread ring smaller in diameter and thereby to make it extend along thecurved first cover. It is not easy to appropriately conduct stitch-downto exhibit desirable tire functions and it also poses a problem inincreasing production efficiency.

For example, stitch-down is conducted while rotating the drum, and,therefore, if the speed of rotation is increased, the shape of low covercomes to be nonuniform and it becomes more difficult to maintain shapeaccuracy. Further, depending on the width of a stitcher roller, defectssuch as scratches and wrinkles may generate on the tread surface. Lowcovers as such have to be discarded as defective products and, hence,production efficiency decreases.

Further, stitcher operation for the stitch-down is complicated andhence, the stitcher must have a complicated structure, increasing costof the equipment.

Therefore, an object of the present invention is to provide a method ofmanufacturing a pneumatic tire having the SOT structure eliminating orminimizing necessity of stitch-down while enabling satisfactoryformation of the low cover, as well as to provide a pneumatic tiremanufactured through this method.

Means of Solving the Problems

The present inventors conducted extensive studies in order to solve theabove problems. As a result, it was found that the above problems can besolved by inventions described below, and thus the present invention hasbeen completed.

The invention according to claim 1 provides a method of manufacturing apneumatic tire having a sidewall-over-tread structure with the sidewallformed to cover tread ends, comprising:

the first cover forming step of wrapping sidewalls on opposite endportions of a first forming drum, pasting an inner liner and a ply onthe center of the first forming drum, setting a pair of beads insidesaid sidewalls, and forming sides of tread by strip-winding on saidsidewalls outer than said beads, and thereby forming a first cover;

the tread ring forming step of successively pasting, on a second formingdrum, a breaker and a band and then forming a center of tread bystrip-winding on said band, and thereby forming a cylindrical treadring;

the shaping step of inserting said first cover inside said tread ring,and inflating that portion of said first cover which is between the saidbeads, and thereby pressure-bonding said tread ring with said firstcover to form a shape of a low cover, and

the turn-up step of turning said sidewalls outside of said beads towardside surfaces of said inflated first cover and pasting said sidewalls onthe side surfaces of said first cover, and bonding said sides of treadon the first cover and said center of tread on said tread ring.

The invention according to claim 2 provides the method of manufacturinga pneumatic tire according to claim 1, wherein

at said turn-up step, said sides of tread of the first cover and saidcenter of tread on said tread ring are bonded, overlapped by at least 5mm in the axial direction of the tire.

The invention according to claim 3 provides the method of manufacturinga pneumatic tire according to claim 1 or 2, wherein at said turn-upstep, a bonding surface of said side of tread of the first cover andsaid center of the tread on said tread ring is approximately vertical tothe outer surface of said tread, or is a tapered surface inclined towardsaid sidewall from the outer surface of said thread to an inner surfaceof said tread.

The invention according to claim 4 provides a pneumatic tire which ismanufactured using the method of manufacturing a pneumatic tireaccording to any one of claims 1 to 3.

Effect of the Invention

By the present invention, a method of manufacturing a pneumatic tirehaving the SOT structure, eliminating stitch-down or minimizingnecessity of stitch-down while enabling satisfactory forming of the lowcover, as well as a pneumatic tire manufactured through this method canbe provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic illustrations showing the first cover forming step ofthe method of manufacturing a pneumatic tire in accordance with anembodiment of the present invention.

FIG. 2 Schematic illustrations showing the tread ring forming step ofthe method of manufacturing a pneumatic tire in accordance with anembodiment of the present invention.

FIG. 3 Schematic illustrations showing the low cover forming step of themethod of manufacturing a pneumatic tire in accordance with anembodiment of the present invention.

FIG. 4 Cross-sectional views schematically showing the turn-up step ofthe method of manufacturing a pneumatic tire in accordance with anembodiment of the present invention.

FIG. 5 Schematic illustrations showing cross section of the treadportion of low cover manufactured using the method of manufacturing apneumatic tire in accordance with an embodiment of the presentinvention.

FIG. 6 Schematic illustrations showing cross section of the treadportion of low cover manufactured using the conventional method ofmanufacturing a pneumatic tire.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention will be described below specifically withreference to the drawings.

Similar to the conventional method of manufacturing a pneumatic tire,the method of manufacturing a pneumatic tire in accordance with thepresent invention includes:

the first cover forming step of forming a first cover on a first formingdrum;

the tread ring forming step of forming a tread ring on a second formingdrum;

the shaping step of inserting said first cover to the inside of thetread ring, inflating the first cover and thereby pressure-bonding itwith the tread ring to attain approximately the shape of a low cover;and

the turn-up step of turning up sidewalls to side surfaces of the firstcover and pasting the sidewalls to cover the tread ends.

The method of manufacturing a pneumatic tire in accordance with thepresent embodiment, however, is different from the conventional methodof manufacturing a pneumatic tire in that the tread is divided to thecenter and sides. Specifically, the method of the present invention isdifferent from the conventional method of manufacturing a pneumatic tirein that:

at the first cover forming step, the sides of tread are formed bystrip-winding on the sidewalls outside the pair of beads;

at the tread ring forming step, the center of tread is formed on theband by strip-winding; and

at the turn-up step, the sides of tread are pasted to the center oftread.

Specific processes of the method of manufacturing a pneumatic tire inaccordance with an embodiment of the present invention will be describedbelow.

(1) First Cover Forming Step

FIG. 1 includes schematic illustrations showing the first cover formingstep of the method of manufacturing a pneumatic tire in accordance withan embodiment of the present invention. As shown in FIG. 1, at the firstcover forming step, first, sidewalls (sw) 34 a, 34 b are wrapped onopposite sides of a first forming drum 30, and then, at the centralportion of first forming drum 30, a sheet-shaped inner liner 32 and aply 35 are pasted.

Next, a pair of beads 36 a, 36 b is set inner than sidewalls 34 a, 34 b.The space between the pair of beads 36 a, 36 b to be set isappropriately selected in accordance with the width of the tire product.

Next, on the sidewalls outside of the pair of beads 36 a, 36 b,strip-shaped tread rubber materials 12 a, 12 b are wound spirally(strip-winding), whereby sides 13 a, 13 b of tread (see FIG. 3) areformed Thus, formation of the first cover 38 is completed. Winding oftread rubber material 12 a, 12 b may be performed before setting thepair of beads 36 a, 36 b.

(2) Tread Ring Forming Step

FIG. 2 includes schematic illustrations showing the tread ring formingstep of the method of manufacturing a pneumatic tire in accordance withan embodiment of the present invention. As shown in FIG. 2, at the treadring forming step, first, two sheet-shaped breakers 22 are wrappedaround and pasted on a second forming drum 20 and, thereafter, JLB(jointless band) 24 is formed by strip-winding on the breaker 22.

Next, on JLB 24, strip-shaped tread rubber material 10 b is wrappedspirally by strip-winding and thus, a center 10 of tread (see FIG. 3) isformed. Thus, forming of tread ring 26 is completed.

(3) Shaping Step

FIG. 3 includes schematic illustrations showing the shaping step of themethod of manufacturing a pneumatic tire in accordance with anembodiment of the present invention. As shown in FIG. 3, at the shapingstep, first, the first cover 38 is inserted to the inside of cylindricaltread ring 26 and combined.

Thereafter, the first cover 38 between the beads 36 a, 36 b is inflated,so that tread ring 26 and the first cover 38 are pressure-bonded, andthe resulting body as a whole is formed to have the shape of a lowcover.

(4) Turn-Up Step

FIG. 4 includes schematic illustrations showing the turn-up step of themethod of manufacturing a pneumatic tire in accordance with anembodiment of the present invention, depicting a right-half of asymmetrical structure. At the turn-up step, as shown in FIG. 4(A),sidewall 34 a outside bead 36 a is turned up and pasted to a sidesurface of inflated first cover 38 and, as shown in FIG. 4(B), the side13 a of tread on the first cover 38 and the center 10 of tread on treadring 26 are bonded together to form tread 1, and thus, formation of thelow cover of pneumatic tire having the SOT structure is completed.

In the foregoing, in order to effectively prevent any gap formed betweenthe side 13 a and the center 10 of tread, which may lead to residualair, it is preferred that the side 13 a and the center 10 of tread arebonded appropriately overlapped in the axial direction of the tire.Specifically, overlapping by at least 5 mm is preferred.

The bonding surface between the side 13 a and the center 10 of treadshould preferably be a substantially vertical surface as shown in FIG.5(A), or a tapered surface, tapered from the upper surface side to theinner surface side of the tread, inclined from the center 10 to thesidewall, as shown in FIG. 5(B) or FIG. 5(C).

(5) Vulcanizing Step

Then, the low cover made in this manner is vulcanized by atire-vulcanizer and a pneumatic tire is manufactured. As shown in FIG.5, the bonded side 13 a and center 10 of tread are formed of rubberhaving the same composition and, therefore, during vulcanization, theseare integrated and form the tread of pneumatic tire. Therefore, by usingthe method of manufacturing a pneumatic tire in accordance with thepresent embodiment, a pneumatic tire having the SOT structure similar tothe conventional pneumatic tire shown in FIG. 6 can appropriately bemanufactured without necessitating the conventional stitch-down step. InFIGS. 5, 1 a, 1 b and 1 c represent various types of treads inaccordance with the present embodiment, and in FIGS. 6, 50 a, 50 b and50 c represent various types of treads in accordance with theconventional method of manufacturing a pneumatic tire.

(6) Effects of the Present Embodiment

As described above, in the present embodiment, the tread, which has beenformed as one body, is formed separately as a center and sides of tread,the center of tread is formed on the tread ring and the sides are formedon the first cover, and these are bonded when the low cover is made.Therefore, various problems occurred in the conventional method ofmanufacturing a pneumatic tire can be solved.

Specifically, during the stitch-down in the conventional pneumatic tiremanufacturing method, the tread ring is made smaller in diameter bycompressing rubber while the drum is being rotated, so as to make thetread extend along the first cover. Therefore, if the speed of rotationis increased, the shape of low cover comes to be non-uniform and itbecomes more difficult to maintain shape accuracy.

If the tread is pulled during the stitch-down, bonding position betweenthe tread and the first cover may possibly deviate. If the tread rubberhas high stiffness, this tendency becomes more noticeable.

Further, depending on the width of stitcher roller, it may slip over thetread surface, possibly causing scratches or wrinkles on the tread.

The low cover having such a problem must be discarded as a defectiveproduct, since such deficiencies affect tire performance such as FV(Force Variation).

If the tread rubber has low stickiness, wound strips may possiblycollapse at the time of stitch-down, making formation of the low coveritself difficult.

In contrast, according to the present embodiment, the tread is formedseparately as a center and sides of tread, the center is formed on thetread ring and the sides are formed on the first cover, and the centerand sides are bonded simultaneously with the turn-up of the first cover,as described above.

As a result, it becomes possible to eliminate or minimize stitch-down,and therefore, the above-described problems such as uneven shape of thelow cover can be prevented. Thus, the shape of low cover can bemaintained with high accuracy, and a pneumatic tire having stable tireperformance such as FV can be manufactured with high efficiency.

The pneumatic tire thus manufactured has the same structure as theconventional tires. The equipment for the stitch-down step can besimplified or made unnecessary, and therefore, production efficiency canfurther be improved.

Further, in the present embodiment, the center of tread is formed tohave the width substantially the same as the breaker or the band, andthe sides of tread that have been subjected to stitch-down are formed onthe first cover. Therefore, unlike the conventional method, thedifficulty of bending rubber of high stiffness along the first cover andpasting it thereon can be avoided. As a result, the first cover and thetread ring can reliably be integrated regardless of the length or gaugeof the tread, and low covers of high quality can be manufactured stablywith high reproducibility.

An end of the tread entering a buttress portion of a pneumatic tire has,depending on its hardness, an influence on steering stability as well asRRC (Rolling Resistance Coefficient of tire) of a vehicle when the tireis mounted. According to the present embodiment, the length or gauge ofthe tread can freely be set and, therefore, such performances canappropriately be attained.

EXAMPLES

1. Formation of Samples

Using the pneumatic tire manufacturing method described in theembodiment above, as samples of each of Examples 1 to 7 and aComparative Example, 100 pneumatic tires having the SOT structure of thesize 215/45R17 were made with the overlaps as shown in Table 1. Further,as samples of a conventional example, 100 pneumatic tires having the SOTstructure were made using the conventional method with a stitcher movedtwo-dimensionally.

In Examples 1, 3 and 7, stitch-down was conducted using a stitcher. InExamples 1 and 7, the stitcher was moved straight (1-dimensional), whilein Example 3, it was moved two-dimensionally, as in the conventionalexample.

2. Evaluation

(1) Low Cover Formation Time

The time necessary for making the low cover of each sample was measured,an average time was calculated for each example, and evaluated as aratio with the time of conventional example being 100.

(2) RFV OA

Overall RFV (Radial Force Variation) of each manufactured pneumatic tirewas measured, and an average was calculated for each example, beingevaluated as a ratio with the value of conventional example being 100.

(3) Frequency of Collapse of Wound Strips

When the low cover of each sample was formed, if the strip-shaped treadmaterial (rubber strip) was collapsed or not was visually inspected, andthe rate (frequency) of collapse was counted for each example.

(4) Variation in Tread Edge Position (R)

Formed pneumatic tires were visually inspected, and deviation of treadedge position from the design value was measured. The average value wascalculated as the variation (R, unit: mm) of the tread edge position.

Results of evaluations described above are as shown in Table 1.

TABLE 1 Prior Example Comparative Art 1 2 3 4 5 6 7 Example Stitcher 2dimensions Straight — 2 dimensions — — — Straight — movement Overlap 5 55 10 15 20 20 0 (mm) Low cover 100 41 28 51 31 30 34 49 49 formationtime (ratio) RFV OA 100 83 72 79 68 76 81 86 103 (ratio) Frequency of 760 0 0 13 18 26 34 0 collapse of wound strips (%) Variation of 5 2 2 2 22 2 2 2 tread edge position (R) (mm)

From Table 1, it can be seen that in any of Examples 1 to 7 andComparative Example, the time necessary for forming the low cover wasshorter than in the conventional example. Therefore, it is understoodthat by forming the tread separately as the sides and center of tread,the low cover can be formed in a shorter time period than by theconventional method.

In Examples 1 to 7 in which the sides and the center of tread wereoverlapped, RFV was lower than the conventional example, whereas inComparative Example in which the sides and the center of tread were notoverlapped (0 mm), RFV was higher than in the conventional example.Therefore, it can be understood that by forming the tread separately asthe sides and the center of tread and bonding these with appropriateoverlapping, a pneumatic tire having improved tire performance can bemanufactured.

Further, in any of the Examples, the frequency of collapse of strips waslower than the conventional example. Thus, it can be understood that thepneumatic tire can be manufactured with higher efficiency than theconventional example. Further, in Examples 1 to 3, collapse of stripsdid not occur at all, and pneumatic tires could be formed reliably.

Further, in any of the Examples, variation of tread edge position wassmall, and it was confirmed that pneumatic tires having superior tireperformance could be manufactured with high reproducibility.

Though collapse of strips was not observed and variation of tread edgeposition was small in Comparative Example, the manufactured pneumatictires had defects of residual air.

The present invention has been described above with reference to theembodiments. However, the present invention is not limited to saidembodiments. Various changes may be made on said embodiments within thescope identical or equivalent to that of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1, 1 a, 1 b, 1 c, 50 a, 50 b, 50 c Tread-   10 Center of tread-   10 b, 12 a, 12 b Strip-shaped tread rubber materials-   13 a, 13 b Side of tread-   20 Second forming drum-   22 Breaker-   24 JLB (jointless band)-   26 Tread ring-   30 First forming drum-   32 Inner liner-   34 a, 34 b Sidewall (sw)-   35 Ply-   36 a, 36 b Bead-   38 First cover-   D1, D2, D3 Overlapping

What is claimed is:
 1. A method of manufacturing a pneumatic tire havinga sidewall-over-tread structure with a sidewall formed to cover treadends, comprising: a first cover forming step of wrapping sidewalls onopposite end portions of a first forming drum, pasting an inner linerand a ply on the center of the first forming drum, setting a pair ofbeads inside said sidewalls, and forming sides of tread by strip-windingon said sidewalls outer than said beads, and thereby forming a firstcover; a tread ring forming step of successively pasting, on a secondforming drum, a breaker and a band and then forming a center of tread bystrip-winding on said band, and thereby forming a cylindrical treadring; a shaping step of inserting said first cover inside said treadring, and inflating that portion of said first cover which is betweenthe said beads, and thereby pressure-bonding said tread ring with saidfirst cover to form a shape of a low cover, and a turn-up step ofturning said sidewalls outside of said beads toward side surfaces ofsaid inflated first cover and pasting said sidewalls on the sidesurfaces of said first cover, and bonding said sides of tread on thefirst cover and said center of tread on said tread ring wherein abonding surface of said sides of tread of said first cover and saidcenter of the tread on said tread ring extends from a radially outersurface of the tread.
 2. The method of manufacturing a pneumatic tireaccording to claim 1, wherein at said turn-up step, said sides of treadof the first cover and said center of tread on said tread ring arebonded, overlapped by at least 5 mm in the axial direction of the tire.3. The method of manufacturing a pneumatic tire according to claim 2,wherein at said turn-up step, the bonding surface of said sides of treadof the first cover and said center of the tread on said tread ring isapproximately vertical to the radially outer surface of said tread, oris a tapered surface inclined toward said sidewall from the radiallyouter surface of said tread to an inner surface of said tread.
 4. Themethod of manufacturing a pneumatic tire according to claim 1, whereinat said turn-up step, the bonding surface of said sides of tread of thefirst cover and said center of the tread on said tread ring isapproximately vertical to the radially outer surface of said tread, oris a tapered surface inclined toward said sidewall from the radiallyouter surface of said tread to an inner surface of said tread.